[DOC] CUDA serialization

[jakirkham]

Would be good to update the serialization docs to include info about custom CUDA serialization.

[quasiben]

@jakirkham can you provide a bit more detail here ? Do you mean the work from #3482 ? Or is there something else you were referring to ?

[jakirkham]

We have a "Dask Serialization Family" section, but nothing about the CUDA Serialization Family. Filling this out would be good.

It may also be worthwhile mentioning what things Dask serializes efficiently (both on the CPU and the GPU) if that's what you are suggesting.

Other thoughts? 🙂